TRANSIENT INCREASE OF FREE CYTOSOLIC CALCIUM DURING NEUTROPHIL MOTILITY RESPONSES

The release of free cytosolic calcium is a secondary messenger for man y cell functions, Here we study the coupling between the release of in tracellular calcium and motility responses of the human neutrophil, Tw o groups of motility responses are studied: motility responses in the presence of adhesion, such as cell crawling and phagocytosis, and moti lity responses 'in suspension', such as pseudopod formation, The motil ity responses are stimulated by the chemoattractant N-formyl-methionyl -leucyl-phenylalanine (fMLP) and the release of calcium is monitored b y measuring the fluorescence from fluo-3, fMLP induces a single releas e of free cytosolic calcium both in suspended cells and in crawling ce lls. Calcium release is a threshold process where the number of cells releasing calcium is dependent on the chemoattractant concentration wh ile the amount of released calcium is not, For suspended cells the thr eshold fMLP concentration for calcium release is in the order of 10(-7 ) M, while for crawling cells it is in the order of 5x10(-9) h, The sm aller value of the threshold fMLP concentration for crawling cells com pared to that for suspended cells suggests that bound adhesion recepto rs are involved in the calcium release. The threshold fMLP concentrati on for suspended cells is also larger than the minimum fMLP concentrat ion (in the order of 10(-10) M) for initiating pseudopod formation. So , there is a range of fMLP concentrations where pseudopod formation oc curs without calcium release, To explore this relationship further, ps eudopod extension and calcium release are stimulated many times in a s ingle cell by using fMLP concentrations above the threshold. The resul t is that calcium release is desensitized by fMLP while pseudopod exte nsion is not, All the results taken together suggest that the release of free cytosolic calcium and the rearrangement of the F-actin network during motility follow different signaling pathways.